The present invention relates to a hydraulic steering system for vehicles utilizing hydraulic steering motors and, more particularly, to a steering system that can be used on agricultural machines, such as tractors, earthmoving machines, or any loading and unloading machine in general.
As is known, steering action consists in selecting the turning direction (right or left), the turning angle (how many degrees each wheel is to be turned with respect to an initial vertical wheel plane), and the speed with which the turning angle is achieved, all of which may be performed by the operator using, for example, a steering wheel connected to a hydraulic steering motor.
In certain operating conditions of the machines referred to above, the operator is forced to turn the steering wheel rapidly to turn the vehicle as quickly as possible.
It should be pointed out that, in this context, the term xe2x80x9cconventional modexe2x80x9d is intended to mean any wheel steering action performed using a steering wheel, a hydraulic steering motor, and a hydraulic steering actuating device, and is normally performed by the operator during normal use of the vehicle, and in particular at fairly high vehicle travelling speeds.
xe2x80x9cFast modexe2x80x9d, on the other hand, is intended to mean a steering mode in which the hydraulic steering motor is in some way bypassed and pressurized oil is fed directly to the steering actuating device. This second mode is designed to reduce the effort required of the operator, especially when maneuvering the vehicle in the farm yard, when making tight U-turns at the end of a field, or in loading applications. In all these situations, xe2x80x9cconventional modexe2x80x9d would call for strenuous, continuous and fast operation of the steering wheel.
In certain recent solutions, to permit easier handling of the steering system, xe2x80x9cjoysticksxe2x80x9d have been provided, which are separate from the steering wheel and are activated by the operator when there is a need to switch from xe2x80x9cconventionalxe2x80x9d to xe2x80x9cfast modexe2x80x9d steering. Joystick devices, however, disconnect the steering wheel completely from the xe2x80x9cfast modexe2x80x9d device.
It would be desirable to provide a steering mechanism that can be utilized with hydraulic steering motors and provide a fast mode of operation.
It is an object of the present invention to provide a steering device for rapidly activating the steering cylinders, but still using a steering wheel as a steering control device in terms of direction, angle and speed.
It is another object of the present invention to provide a fast steering system where the fast mode of operation can only be implemented at low vehicle travelling speeds.
It is still another object of the present invention to provide a fast mode control device located on the vehicle steering wheel itself.
It is an advantage of this invention that the steering can be controlled at all times from the steering wheel, even when in a fast mode of operation.
It is another advantage of this invention that the system can be configured so that the fast mode of operation can be implemented only by first pushing a fast mode button and then turning the steering wheel.
It is a feature of this invention that the release of the push button for implementing the fast mode of operation will restore the normal mode of operation of the steering system.
It is still another advantage of this invention that the release of the push button for implementing the fast mode of operation will immediately restore the normal mode of operation of the steering system.
In is another feature of this invention that a failure of the hydraulic pump allows for an emergency steering mode of operation.
It is still another feature of this invention that a spring 41 of the change valve 40 and the depressurization of the drive conduit 79 upon failure of the hydraulic pump ensure that the manual emergency steering mode of operation can be restored to the steering system.
It is yet another feature of this invention that the fast mode of operation can only be implemented only at low vehicle speed under the control of an electronic control unit.
It is yet a further feature of this invention that the fast mode of operation can be engaged by activating a button located on the steering wheel, or at any point in the cab within easy reach of the operator.
It is yet another advantage of this invention that the fast mode of operation can be selectively and conveniently engaged.
According to the present invention, there is provided a hydraulic steering system having a fast steering mode the in which the same steering mechanism is operable to select the turning direction, the turning angle, and the speed with which said turning angle is reached.
These and other objects, features and advantages are accomplished according to the instant invention by providing a hydraulic steering system for a tractor which can be operated in a conventional steering mode or in a fast steering mode. In the conventional steering mode of operation, a conventional steering wheel and steering motor direct pressurized oil to the steerable wheels for selecting the turning direction, the turning angle, and the speed with which the turning angle is achieved. In the fast steering mode of operation, a fast-turning valve is controlled by the operator to direct oil directly to the steerable wheels, thereby by-passing the steering motor. The conventional steering wheel and steering motor continue, however, to control the steering operation as in the conventional steering mode of operation.